Bonded nonwoven fabrics



United States Patent 3,498,875 BONDED NONWOVEN FABRICS Martin K.Lindemann, Somerville, and Rocco P. Volpe,

Newark, N.J., assignors, by mesne assignments, to Cumberland ChemicalCorporation, New York, N.Y., a corporation of Delaware N0 Drawing. FiledMar. 31, 1965, Ser. No. 444,401 Int. Cl. D04h 1/64; B32b 5/02 US. Cl.161170 3 Claims ABSTRACT OF THE DISCLOSURE A latex compositioncomprising an aqueous medium having colloidally suspended in it anemulsion-polymerized interpolymer of vinyl acetate, ethylene andglycidyl acrylate, the interpolymer containing 5 to 40% ethylene and atleast about 0.5% glycidyl acrylate, is used to make non-woven fabricsfrom a loosely assembled mass of fibers, the interpolymer deposited fromthe latex being effective as a binder for the fibers.

This invention relates to so-called nonwoven fabrics of the typecomposed of loosely assembled webs of fibers bound together with anadhesive binder, and is more particularly concerned with cellulosicnonwoven fabrics bound by a binder which is a modified copolymer ofvinyl acetate.

Adequately bonded nonwoven fabrics have advantages over woven fabricsfor a large variety of uses. Bonded non-woven fabrics have heretoforebeen formed by impregnating, printing or otherwise depositing anadhesive bonding material on a base web predominantly comprisingrelatively long fibers, including those of textile length of from about/2 inch to about 2 /2 inches, or more. The base web of nonwoven fibers,to which the binder is applied, can be produced inexpensively and withlow capital investment by carding, garnetting, air-laying, papermakingprocedures, or'other known operations for which efiicient automation ispossible. The operation of bond ing the fibers in place is much lessexpensive than conventional spinning and weaving. In comparison withwoven fabric, the bonded nonwoven fabrics can be made in a much greaterrange of thicknesses per unit weight, with more homogeneous structures,no unraveling tendency, and with greater water absorbency, porosity andresiliency, when required.

Generally speaking, it is desirable to produce a soft fabric with asmuch strength as possible. The choice of the bonding agent is veryimportant in obtaining both softness and strength. Many bonding agentswhich are used in the art, such as polyvinyl acetate, have adequatebonding strength when dry, but lose a major proportion of this strengthwhen the fabric is wetted with water. This wet strength may be definedas the ability of the fabric to retain part of its dry strength aftersubstantially complete saturation with water. This property of wetstrength is very important when the fabric is to be used in any mannerwhere it will become moist or will come into contact with fluids, e.g.when it is used as a towel, as a disposable diaper, or the like.

In order to obtain fabrics which are textile-like in quality, havingdrape, flexibility, and softness, the polyvinyl acetate resins have beensoftened with external plasticizers such as dibutyl phthalate beforeapplication to the web, or the vinyl acetate has been copolymerized withinternally plasticizing comonomers such as the alkyl acrylates, thealkyl methacrylates, vinyl stearate, or the dialkyl fumarates ormaleates. The internally plasticized copolymers impart to the resultingfabric somewhat improved wet strength and wet abrasion resistance overthe 3,498,875 Patented Mar. 3, 1970 "ice use of externally-plasticizedhomopolymers as binders, but still greater wet strength at highflexility is desired for the widest use of these fabrics.

Considerable time and effort have also been expended on developingtechniques for improving the wet strength of bonding agents for nonwovenfabrics consisting predominantly of cellulose fibers. One of the moreimportant developments in this field has been the treatment of thefabrics with aminoaldehyde condensation products such asurea-formaldehyde and melamine-formaldehyde, along with heat and acatalyst to set the resin and crosslink the cellulose fibers. Suchtreatments, however, although they increase wet strength, are relativelycostly and complicated, reduce the softness of the fabric, and tend tohave a detrimental odor due to the release of formaldehyde.

It is accordingly an object of this invention to provide new, improvedpolymeric binders for nonwoven fabrics.

Another object of the invention is to provide relatively low-cost,binder-containing nonwoven fabrics of enhanced wet strength and otherdesirable properties.

In accordance with this invention it has been found that these andrelated objects are achieved by a binder for nonwoven fabrics which isan interpolymer of vinyl acetate and ethylene copolymerized withglycidyl acrylate which is effective to polymerize and to cross-linkwith the initial vinyl acetate and ethylene containing interpolymerunder the action of heat. The above-described binder is applied to thefiber web to bind the fibers together into the desired nonwoven fabricin the form of an aqueous latex containing the interpolymer of vinylacetate, ethylene and copolymerized glycidyl acrylate in the dispersedphase. The vinyl acetate-ethylene-glycidyl acrylate interpolymer ischaracterized by an ethylene content of 5 to 40%, preferably 16 to 40%,a particle size of 0.1 to 2 preferably 0.1 to 0.25 and an intrinsicviscosity of 1 to 2.5 dl./ g. The amount of glycidyl acrylate is 0.5 to10% based on the vinyl acetate.

The binder is readily prepared by the interpolymerization of vinylacetate, ethylene and glycidyl acrylate in an aqueous dispersion system.The glycidyl acrylate readily copolymerizes with the vinyl acetate andthe ethylene to form an interpolymer or terpolymer but, as mentioned, isadapted to undergo further reaction after this initial polymerizationupon the application of heat in the processing of the nonwoven fabric tofurther cross-link the interpolymer. Particularly suitable as thebinderis a vinyl acetate-ethylene-glycidyl acrylate interpolymer latex whichis prepared by the following process.

Vinyl acetate and ethylene are copolymerized in the presence of theglycidyl acrylate in an aqueous medium under pressures not exceedingatmospheres in the presence of a catalyst and at least one emulsifyingagent. the aqueous system being maintained, by a suitable bufferingagent, at a pH of 2 to 6, the catalyst being added incrementally. Theprocess is a batch process which involves first a homogenization periodin which the vinyl acetate suspended in water is thoroughly agitated inthe presence of ethylene under the working pressure to effect solutionof the ethylene in the vinyl acetate up to the substantial limit of itssolubility under the conditions existing in the reaction zone, while thevinyl acetate is gradually heated to polymerization temperature. Thehomogenization period is followed by a polymerization period duringwhich the catalyst, which consists of a main catalyst or initiator, andmay include an activator, is added incrementally, and the glycidylacrylate is similarly added incrementally, the pressure in the systembeing maintained substantially constant by application of a constantethylene pressure.

Various free-radical forming catalysts can be used in carrying out thepolymerization of the monomers, such as peroxide compounds. Combinationtype catalysts employing both reducing agents and oxidizing agentscanalso be used. The use of this type of combined catalyst is generallyreferred to in the art as redox polymerization or redox system. Thereducing agent is also often referred to as an activator and theoxidizing agent as an initiator. Suitable reducing agents or activatorsinclude bisulfites, sulfoxylates, or other compounds having reducingproperties such as ferrous salts, and tertiary aromatic amines, e.g.N,N-dimethyl aniline. The oxidizing agents or initiators includehydrogen peroxide, organic peroxides such as benzoyl peroxide, t-butylhydroperoxide and the like, persulfates, such as ammonium or potassiumpersulfate, perborates, and the like. Specific combination typecatalysts or redox systems which can be used include hydrogen peroxideand zinc formaldehyde sulfoxylate; hydrogen peroxide, ammoniumpersulfate, or potassium persulfate, with sodium metabisulfite, sodiumbisulfite, ferrous sulfate, dimethyl aniline, zinc formaldehydesulfoxylate or sodium formaldehyde sulfoxylate. Other types of catalyststhat are well-known in the art can also be used to polymerize themonomers, such as the peroxide compounds, with or without the additionof reducing agents or other activating materials. It is advantageous toutilize more water-soluble peroxides, such as hydrogen peroxide, ratherthan the more oil-soluble peroxides such as t-butyl hydroperoxide, inthe redox system, to catalyze the monomer polymerization. Redox catalystsystems are described, for example, in Fundamental Principles ofPolymerization by G. F. DAlelio (John Wiley and Sons, Inc., New York,1952) pp. 333 et seq. Other types of catalysts that are well-known inthe art can also be used to polymerize the monomers according to thisinvention, with or without the addition of reducing agents or otheractivating materials.

The catalyst is employed in the amount of 0.1 to 2%, preferably 0.25 to0.75%, based on the weight of vinyl acetate introduced into the system.The activator is ordinarily added in aqueous solution and the amount ofactivator is generally 0.25 to 1 times the amount of catalyst.

The emulsifying agents which are suitably used are non-ionic. Suitablenon-ionic emulsifying agents include polyoxyethylene condensates.Polyoxyethylene condensates may be represented by the general formula:

Where R is the residue of a fatty alcohol containing 10-18 carbon atoms,an alkyl phenol, a fatty acid containing 10-18 carbon atoms, an amide,an amine, or a mercaptan, and where n is an integer of 1 or above. Somespecific examples of polyoxyethylene condensates which can be usedinclude polyoxyethylene aliphatic ethers such as polyoxyethylene laurylether, polyoxyethylene oleyl ether, polyoxyethylene hydroabietyl etherand the like; polyoxyethylene alkaryl ethers such as polyoxyethylenenonylphenyl ether, polyoxyethylene octylphenyl ether and thelike;'polyoxyethylene esters of higher fatty acids such aspolyoxyethylene laurate, polyoxyethylene oleate and the like as well ascondensates of ethylene oxide with resin acids and tall oil acids;polyoxyethylene amide and amine condensates such as N-polyoxyethylenelauramide, and N-lauryl-N-polyoxyethylene amine and the like; andpolyoxyethylene thio-ethers such as polyoxyethylene n-dodecylthio-ether.

The non-ionic emulsifying agents which can be used according to thisinvention also include a series of surface active agents known asPluronics. The Pluronics have the general formula:

where a, b and c are integers of 1 or above. As b increases, thecompounds become less water soluble or more oil soluble and thus morehydrophobic when a and remain substantially constant.

In addition, highly suitable are a series of ethylene 4 oxide adducts ofacetylenic glycols sold commercially under the name Surfynols. Thisclass of compounds can be represented by the formula in which R and Rare alkyl radicals containing from 3 to 10 carbon atoms, R and R areselected from the group consisting of methyl and ethyl, x and y have asum in the range of 3 to 60, inclusive.

Some examples of non-ionic emulsifying agents which can be used are asfollows:

A polyoxyethylene nonylphenyl ether having a cloud point of between 126and 133 F. is marketed under the trade name Igepal CO-630 and apolyoxyethylene nonylphenyl ether having a cloud point above 212 F. ismarketed under the trade name Igepal CO-887. A similar polyoxyethylenenonylphenyl ether having a cloud point of about 86 F. is marketed underthe trade name Igepal CO-6l0. A polyoxyethylene octylphenyl ether havinga cloud point of between F. and 160 F. is marketed under the trade nameTriton X-lOO.

A polyoxyethylene oleyl ether having a cloud point of between 80 F. and160 F. is marketed under the trade name Atlas G39'15 and apolyoxyethylene lauryl ether having a cloud point above 190 'F. ismarketed under the trade name Brij 35.

A polyoxypropylene having a cloud point of about F. is marketed underthe trade name Pluronic L-64, and a polyoxypropylene having a cloudpoint of about 212 F. is marketed under the trade name Pluronic F-68.Pluronic L-64 is a polyoxyethylene-polyoxypropylene glycol conforming tothe above general formula for Pluronics in which the polyoxypropylenechain has a molecular weight of 1500 to 1800 and the polyoxyethylenecontent is from 40 to 50 percent of the total weight of the molecule.Pluronic F-68 is a polyoxyethylenepolyoxypropylene glycol conforming tothe above general formula for Pluronics in which the polyoxypropylenechain has a molecular weight of 1500 to 1800 and the polyoxyethylenecontent is from 80 to 90 percent of the total Weight of the molecule.The polyoxypropylene Pluronics are obtained by condensing ethylene oxideon the polyoxypropylene base and the hydrophobic-hydrophilic nature ofthe resulting compound is controlled by varying the molecular weight ofeither the hydrophobic base or the hydrophilic portion of the molecule.

Representative of the Surfynols are Surfynol 465 which is an ethyleneoxide adduct of 2,4,7,9-tetramethyl decynediol containing an average of10 moles of ethylene oxide per mole, and Surfynol 485 which correspondsto Surfynol 465 but contains an average of 30 moles of ethylene oxideper mole. Surfynol 465 has a cloud point of about F. and Surfynol 485has a cloud point above 212 F.

In the foregoing, cloud points recited are based on 1% aqueoussolutions. A single emulsifying agent can be used, or the emulsifyingagents can be used in combination. When combinations of emulsifyingagents are used, it is advantageous to use a relatively hydrophobicemulsifying agent in combination with a relatively hydrophilic agent. Arelatively hydrophobic agent is one having a cloud point in 1% aqueoussolution below F. and a relatively hydrophilic agent is one having acloud point in 1% aqueous solution of 190 F. or above.

The concentration range of the total amount of emulsifying agents usefulis from 0.5 to 5% based on the aqueous phase of the latex regardless ofthe solids content. Latex stabilizers are also advantageously used. Thestabilizers employed are, in part, governed by the use to which thecopolymer latex is to be put, and/or the particle size of the copolymer.For example, the vinyl acetate ethylene copolymer latices prepared bythe method described can have various average particle size ranges. Whenthe latices are to have a small average particle size, e.g. below 025 aspreferred in the present invention, an ethylenicallyunsaturated acidhaving up to 6 carbon atoms, is advantageously used as the stabilizer.Typical acids of this character are acrylic acid, methacrylic acid,itaconic acid, maleic acid, vinyl sulfonic acid and the like. Theseunsaturated acids impart increased stability to the latices. They tendto copolymerize with the monomers in the system. The amount ofunsaturated acid used is suitably 0.1 to 3% based on vinyl acetate,preferably 0.2 to 1%.

On the other hand, when the latex has an average particle size above0.25 a protective colloid can be used in the polymerization mixture asthe stabilizing agent, although an unsaturated acid can be used ifdesired. Various amounts of colloids can be incorporated into thelatices as desired, but it is preferred to maintain the colloidconcentration at the lowest level possible. The amount of colloid usedwill also depend upon the particular colloid employed. Colloids ofhigher molecular weight tend to produce a latex of a higher viscositythan like amounts of a lower molecular weight colloid. Other propertiesof the colloids aside from their molecular weight also affect theviscosity of the latices and also the properties of the films formedtherefrom. It is advantageous to maintain the colloid content of thelatices between about 0.05 and 2% by weight based on the total latex,and hydroxyethyl cellulose is a particularly advantageous colloid whenused in the latices.

Various other colloids can also be used, including polyvinyl alcohol,partially-acetylated polyvinyl alcohol, e.g. up to 50% acetylated,casein, hydroxyethyl starch, carboxymethyl cellulose, gum arabic, andthe like, as known in the art of synthetic polymer latex technology.

In order to maintain the pH of the system at the desired value, there issuitably added an alkaline buffering agent of any convenient type. Anyalkaline material which is compatible with the stabilizing agent can beused as the butter. The amount of butter is that sufiicient to adjustthe pH of the system within the desired range. Ammonium and sodiumbicarbonate are preferred bulfers because of their compatibility withthe system and their low cost. The amount of buffer is generally about0.1 to 0.5% by weight, based on the monomers. Other buffers such asdisodium phosphate, sodium acetate, and the like, can, however, also beused.

One of the features of the method described above is that latices ofrelatively high solids contents can be directly produced and thus theproducts generally have, as produced, solids contents of 45 to 60%. Theycan, of course, be easily thinned by the addition of water to lowersolids contents of any desired value.

Lower reaction temperatures for polymerizing vinyl acetate than haveheretofore been feasible economically can also be used. The use of lowerreaction temperatures has been found to result in higher molecularweight vinyl acetate copolymers. The reaction temperature can becontrolled by the rate of catalyst addition and by the rate of the heatdissipation therefrom. Generally we have found that it is advantageousto maintain a mean temperature of about 50 C. during the polymerizationof the monomers and to avoid temperatures much in excess of 80 C. Whiletemperatures as low as 0 can be used, economically the lower temperaturelimit is about 30 C.

The reaction time will also vary depending upon other variables such asthe temperature, the catalyst, and the desired extent of thepolymerization. It is generally desirable to continue the reaction untilless than 0.5% of the vinyl acetate and the glycidyl acrylate remainsunreacted. Under these circumstances, a reaction time of about 6 hourshas been found to be generally sufficient for complete polymerization,but reaction times ranging from 3 to 10 hours have been used, and otherreaction times can be employed, if desired.

In carrying out the polymerization, a substantial amount of the vinylacetate is initially charged to the polymerization vessel and saturatedwith ethylene in the manner discussed above. Most advantageously, atleast about 75% of the total vinyl acetate to be polymerized isinitially charged, preferably at least about and the remainder of thevinyl acetate is incrementally added during the course of thepolymerization. The charging of all of the vinyl acetate initially isalso contemplated, with no additional incremental supply. When referenceis made to incremental addition, whether of vinyl acetate, the glycidylacrylate, catalyst, or activator, substantially uniform additions, bothwith respect to quantity and time, are contemplated.

The quantity of ethylene entering into the copolymer is influenced bythe pressure, the agitation, and the viscosity of the polymerizationmedium. Thus, to increase the ethylene content of the copolymer, higherpressures are employed, but even to introduce 40% or more of ethyleneinto the copolymer, pressures in excess of atms. are not required.However, a pressure of at least about 10 atms. is most suitablyemployed. Similarly, when high ethylene contents are desired, a highdegree of agitation should be employed, and high viscosities should beavoided, a low viscosity being preferred. When referring to viscosities,a viscosity of 30 to centipoises is considered a low viscosity, aviscosity of 151 to 800 centipoises is considered a medium viscosity,and a viscosity of 801 to 3000 centipoises is considered a highviscosity.

The process of forming the vinyl acetate-ethyleneglycidyl acrylateinterpolymer latices generally comprises the preparation of an aqueoussolution containing at least some of the emulsifying agent andstabilizer, and the pH buffering system. This aqueous solution and theinitial charge of vinyl acetate are added to the polymerization vesseland ethylene pressure is applied to the desired value. As previouslymentioned, the mixture is thoroughly agitated to dissolve ethylene inthe vinyl acetate and in the water phase, agitation being continueduntil substantial equilibrium is achieved. This generally requires about15 minutes. However, less time may be required depending upon thevessel, the efiiciency of agitation, the specific system, and the like.In any case, by measuring the pres sure drop of the ethylene inconventional manner, the realization of substantial equilibrium can beeasily determined. Conveniently the charge is brought to polymerizationtemperature during this agitation period. Agitation can be effected byshaking, by means of an agitator, or other known mechanism. Thepolymerization is then initiated by introducing initial amounts of thecatalyst, and of the activator when used. After polymerization hasstarted, the catalyst and the activator are incrementally added asrequired to continue polymerization, and the glycidyl acrylate and theremaining vinyl acetate, if any, is similarly added.

As mentioned, the reaction is generally continued until the residualvinyl acetate and the glycidyl acrylate content is below 0.5 Thecompleted reaction product is then allowed to cool to about roomtemperature, while sealed from the atmosphere. The pH is then suitablyadjusted to a value in the range of 4.5 to 7, preferably 6 to 6.5 toinsure maximum stability.

The particle size of the latex can be regulated by the quantity ofnon-ionic emulsifying agent or agents employed and by the use or nonuseof a colloidal stabilizing agent. Thus, to obtain smaller particlesizes, greater amounts of emulsifying agent are used and colloidalstabilizing agents are not employed. For example, to provide averageparticle sizes below about 0.25 the total amount of non-ionicemulsifying agent should be at least about 2%, based on the aqueousphase of the latex, and no colloidal stabilizing agent should be used,or if a colloidal stabilizing agent is used, only very small amountsshould be employed.

On the other hand, when particle sizes of 0.25/1. and

above are desired, at most about 2% of total emulsifying agent based onthe aqueous phase of the latex should be used, and a colloidalstabilizing agent should be included in the amounts previouslyindicated. As a general rule, the smaller the amount of emulsifyingagent employed and the greater the amount of colloidal stabilizing agentincluded in the latex system, the greater the average particle size.Conversely, the greater the amount of the emulsifying agent employed andthe smaller the amount of collodial stabilizing agent used, includingthe total absense of the latter, the smaller the average particle size.It will be understood that in each case, the quantity and size valuesreferred to above are all within the ranges of values previouslyspecified.

By following the procedure described above, particularly the initialsaturation of the polymerization mixture with ethylene beforepolymerization is initiated, there can be produced the stable vinylacetate-ethylene-glycidyl acrylate interpolymer latex characterizedabove, with the copolymer having an ethylene content of to 40%, anintrinsicviscosity of l to 2.5 dl./g., and an average particle size of0.1 to 2 and the latex having a high solids content of up to 60% ormore.

The ethylene content can be determined by means of the saponificationnumber.

Intrinsic viscosity is suitably determined by conventional techniques,e.g. in accordance with the procedures described on pages 309*314 ofPrinciples of Polymer Chemistry by Paul J. Flory (Cornell UniversityPress 1963); using an Ubbelohde (suspended level) Viscometer at 30 C.

The vinyl acetate-ethylene-glycidyl acrylate binder described above issuitably used to prepare nonwoven fabrics by a variety of methods knownto the art which, in general, involve the impregnation of aloosely-assembled mass of fibers with the binder latex, followed bymoderate heating to dry the mass. In the case ofthe present inventionthis moderate heating also serves to cure the binder by forming across-linked interpolymer. Before the binder is applied it is, ofcourse, mixed with a suitable catalyst for the glycidyl acrylate. Thus,basic catalysts such as organic amines, e.g. ethylenediamine andpiperidine, or metal salts of weak acids, such as sodium acetate or zincfluoborate are suitably used, as known in the art. The amount ofcatalyst is generally about 0.5 to 2% of the total resin.

The starting layer or mass can be formed by any one of the conventionaltechniques for depositing or arranging fibers in a web or layer. Thesetechniques include carding, garnetting, air-laying, and the like.Individual webs or thin layers formed by one or more of these techniquescan also be laminated to provide a thicker layer for conversion into afabric. In general, the fibers extend in a plurality of diversedirections in general alignment with the major plane of the fabric,overlapping, intersecting and supporting one another to form an open,porous structure. When reference is made to cellulose fibers, thosefibers containing predominantly C H O groupings are meant. Thus,examples of the fibers to be used in the starting layer are the naturalcellulose fibers such as cotton and hemp and the synthetic cellulosefibers, such as rayon, and regenerated cellulose. Often the fibrousstarting layer contains at least 50% cellulose fibers, whether they benatural or synthetic, or a combination thereof. Other fibers in thestarting layer may comprise natural fibers such as wool, or jute;artificial fibers such as cellulose acetate; synthetic fibers such aspolyamides, i.e. nylon, polyesters, i.e. Dacron, acrylics, i.e. Dynel,Acrilan, Orlon, polyolefins, i.e. polyethylene, polyvinyl chloride,polyurethane, etc., alone or in combination with one another.

The fibrous starting layer or web suitably weighs from about 100 grainsto about 2,000 grains per square yard and preferably weighs about 200grains to about 800 grains per square yard. This fibrous starting layer,re-

gardless of its method of preparation, is then subjected to at least oneof the several types of bonding operations to anchor the individualfibers together to form a selfsustaining web. Some of the better-knownmethods of bonding are overall impregnation, or printing the web withintermittent or continuous straight or wavy lines or areas of binderextending generally transversely or diagonally across the web andadditionally, if desired, along the web.

The amount of binder, calculated on a dry basis, applied to the fibrousstarting web, suitably ranges from about 20 to about or more by Weightof the starting web, and preferably from about 35 to about 50% by weightof the starting web. The impregnated web is then dried and cured. Thus,the fabrics are suitably dried by passing them through an air oven orthe like and then through a curing oven. Ordinarily, drying is effectedat -200 F. for 4-6 min., followed by curing at 300-310 F. for 3-5 min.or more. However, other time-temperature relationships can be employed,as is well known in the art, shorter times at higher temperatures orlonger times at lower temperatures being used. For example, the curingstep can be carried out at 280 F. for about 15 min. or more. However,economic considerations make the use of excessively long timesundesirable, and the upper temperature limit is governed by the natureof the fibers. Temperatures which degrade the fibers are, of course,avoided. However, if the fibers are heat resistant, temperatures even ashigh as 350 F. or higher can be used with times of 5-10 min. or more. Insome cases, if desired, the drying and curing can be effected in asingle exposure or step, e.g. at 300 F. for 5-10 min.

Nonwoven fabrics prepared in accordance with this invention have wetstrength values as great as the usual woven cotton fabrics. In addition,these nonwoven fabrics have the outstanding advantage of low cost, bothin comparison with woven fabrics and with nonwoven fabrics prepared withbinders previously available.

External plasticizers are not needed with the binders of this invention,which greatly simplifies the preparation of nonwoven fabrics. However,they can be used to modify the properties of the fabrics when desired.Thus some external plasticizers can be added when an extremely softfabric is desired.

Thus, it has been observed that the flexibility of the fabric can beincreased by the addition of a hydrophobic external plasticizer to thebinder composition without loss of desirable properties. Examples ofexternal plasticizers which are suitably used includedibutoxyethylphthalate, dibutyl phthalate, tricresyl phosphate, and lowmolecular weight polyesters.

These external components may be added just before application, if theirstability in the dispersion or solution is low, or they may beformulated into the aqueous dispersion of the binder and stored if thestability in aqueous dispersion is high.

The following examples are given to illustrate the present invention,but it will be understood that they are intended to be illustrative onlyand not limitative of the invention. In the examples, all parts are byweight unless otherwise indicated.

Example 1 The following was charged to a 25 gal. stainless steelpressure reactor equipped with temperature controls and an agitator:

After purging with nitrogen and ethylene, 104 g. potassium persulfatewas added to the mixture. The agitator was set at 300 rpm. and thekettle pressurized with ethylene to 40 atm. After reaching equilibriumand after heating to 50 C. the agitation was reduced to 195 r.p.m. andpolymerization was started by adding 20 cc. of a 0.5% solution ofFormopon. During the polymerization 139 g. of maleic acid and 1800 g. ofglycidyl acrylate were added incrementally, in addition to 136 g. ofpotassium persulfate which was also added incrementally as needed. Thepolymerization was complete after 4 /2 hrs. The latex was cooled andneutralized with ammonias to a pH of 5.2. The latex had the followingproperties:

Intrinsic viscosity- 0.57 (100 ml./g., benzene, 30 0). Particlesize=less than 0.18,.

The above-described latex was diluted to solids, 2% of sodium acetate(based on the weight of solids) was added and the latex applied to anon-woven web of 50% viscose rayon-50% cellulose acetate fibers, using aButterworth three-roll padder. The latex was applied at the rate ofabout 18% (solids) based on the weight of the web. The web was thendried and cured on a pin frame at 300 F. for 6 min. and then for 10 min.at 350 F.

The cured web was then subjected to a l-hr. acceierated washing test ata temperature of 160 F. employing an AATCC L-aunder Ometer, inaccordance with Standard Test Method 61-1962 as set forth on pages B-76and B-77 of the 1962 Technical Manual of the American Association ofTextile Chemists rand Colorists, with the sample being tumbled in astainless steel cylinder containing 100 stainless steel balls and theWash Solution. The web was found to be completely intact after thewashing operation.

Example 2 The above-described procedures with respect to the preparationof a bonded non-woven fiber web were repeated, except that the binderused was a vinyl acetate homopolymer latex initially having a solidscontent of 10 48.7 and a pH of 66.5. At the end of the washing test, theweb was no longer intact and had failed the test.

In the characterization of the interpolymer of Example 1, T is thetemperature at which the torsional modulus is 135,000 lbs./in. and T thetemperature at which the torsional modulus is 10,000 lbs/in. determinedaccording to ASTM-D104361T.

It will be apparent that various changes and modifications may be madein the embodiments of the invention described above, without departingfrom the scope of the invention, as defined in the appended claims, andit is intended, therefore, that all matter contained in the foregoingdescription shall be interpreted as illustrative only and not aslimitative of the invention.

We claim:

'1. A non-woven fabric formed from a loosely assembled Web of fibersbonded together with a binder comprising an emulsion-polymerizedinterpolymer of vinyl acetate, ethylene, and a glycidyl acrylate, saidinterpolymer containing 5 to 40% ethylene and a minor amount of glycidylacrylate of at least about 0.5% u to about 10% based on the vinylacetate.

2. A non-woven fabric formed from a loosely assembled web of fibersbonded together by a binder deposited from a vinylacetate-ethylene-glycidyl acrylate interpolymer latex comprising anaqueous medium having colloidally suspended therin an interpolymer ofvinyl acetate, ethylene, and glycidyl acryl ate, said interpolymercontaining 5 to 40% ethylene and a minor amount of glycidyl acryl'ate ofat least about 0.5% up to about 10% based on the vinyl acetate.

3. A non-woven fabric as defined in claim 2 wherein said vinylacetate-ethylene-glycidyl aorylate inter-polymer has a particle size of0.1 to 2 References Cited UNITED STATES PATENTS 3/1963 Adelman 26080.728/1965 Heino 2'6080.72

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3, 9 75Dated March 3, 1970 Inventor) Martin K. Lindemann and Rocco P. Volpe Itis certified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In the heading change "Cumberland Chemical Corporation,

New York, N.Y. a corporation of Delaware" to Air Reduction Company,Incorporated, New York, N.Y., a. corporation of New York Col. 2, line53, the period at the end of the line should be a. comma Col. 9, line30, the word "acceiereted" should read accelerated Col. 10, line 27, theword 'therin" should read therein SIGNED RND SEALED Atteat:

wmrm E. sum. 3 Fletcher, I Wagoner of Patents Aflesting Officer FORMPC4050 (IO-69] ugcom -pc 593154559 u.i. covunulm' "mime omcl m9 o-u|-lu

